At moderate climb angles, and as long as you are not totally dangling on
the end a bit or rope (as in a helicopter lift), the glider is essentially
still in free flight during an aerotow. To produce enough lift to climb,
the glider's wing must be at a higher angle of attack for a given
airspeed than it would be in normal gliding flight. Therefore the airspeed
at which the wing stalls must be higher.

Or looking at it another way, the wing has to support the normal weight of
the glider and its occupants, plus the component of the weight acting
backwards and downwards, so an effective increase in wing loading.

Quite a few pilots who have aerotowed behind motorgliders and other slow,
low powered, tugs have commented on how the glider feels uncomfortably
close to the stall, even when the airspeed is a least 10 knots above the
normal stalling speed, so I am reasonably sure that this is a real effect.


Derek Copeland


At 18:19 13 March 2009, Mike Schumann wrote:
Running out of elevator authority is very different then stalling. A
glider
stalls when the angle of attack increases past a critical point.
Reducing

the angle of attack, increases your stall margin.

Mike Schumann

"Mike the Strike" wrote in message
...
On Mar 11, 6:33 pm, "Mike Schumann" wrote:
I can't imagine why the stall speed would change on tow. The controls
may
feel different because the tow rope is pulling on the nose, so any
attempt
to turn or change the angle of attack will face an increased counter
force,
but that's different than a change in the stall speed of the glider.

Read my earlier post!

The tow rope in some gliders (especially those standard class racing
gliders with a shallow angle of incidence) acts to pull the nose down,
reducing the angle of attack of the wing and tailplane. The stall
speed depends not only on speed, but angle of attack - if you reduce
it by pulling down on the nose, lift will be reduced. As I mentioned
earlier, the Discus 2 runs out of elevator authority somewhere below
60 knots and descends into low tow, even though its free-flight stall
speed is less than 40 knots. It's not just a difference of feel - the
glider wallows and almost becomes uncontrollable.

Mike